Functionalized vegetable oils have been extensively used for various applications, such as coatings, inks, and agrochemicals. They can also be functionalized by epoxidation with organic peracids or H2O2. These epoxidized vegetable oils show excellent utility as inexpensive, renewable materials for industrial applications.
The most commonly utilized epoxidized oil is epoxidized soybean oil (ESO), that is soybean oil whose double bonds have been converted to epoxy (oxirane) groups. These products are used as plasticizers for poly(vinyl chloride) (PVC) polymers and copolymers. The ESO also serves to stabilize the vinyl resin. Epoxidized linseed oil (ELO) is also used with bisphenol epoxy resins to increase the flexibility of amine cured epoxy polymers. Epoxidized linseed oil can be further functionalized by reacting with such materials as acrylic acid. The acrylated oil is used in ultraviolet (uv) curing inks. Epoxidized and other types of functionalized vegetable oils have many other industrial, non-food applications which are sensitive to the presence of residual peroxide which can have undesirable effects in the final products. Thus it is desirable to reduce the residual peroxide levels to a minimum for optimum consistency of properties of the epoxidized oil products.
Hydrogen peroxide is widely used in the commercial epoxidation of vegetable and other plant-derived oils due to the capability of hydrogen peroxide to react with unsaturated substances in the oils to yield oxirane (1,2-epoxy) compounds and/or 1,2-glycols, dependent upon reaction conditions. These reactions, known as epoxidation and hydroxylation, respectively, are similar in many respects including the similarity of preparative methods; and the ease of transition from 1,2-epoxy compounds, for example, to the corresponding glycols. Available methods for preparing epoxy compounds and glycols, via reaction of a peroxygen compound with an olefinic material, include reactions utilizing alkaline hydrogen peroxide, hydrogen peroxide in anhydrous tertiary alcohols, hydrogen peroxide in the presence of light, and organic peracids. These synthetic routes are all useable to make epoxidized vegetable oils. At the conclusion of the epoxidation reaction, residual peroxide and peroxide derived radicals may unavoidably remain in the finished epoxidized vegetable oil. Many end uses find elevated levels of residual peroxide to have potentially detrimental effects on the final product and processes of making the final product. It would be desirable to have a simple method for removing or deactivating residual peroxide.
Vegetable oils which are polyunsaturated, especially safflower oil, sunflower seed oil, soybean oil and corn oil are particularly susceptible to hydroperoxide formation. Polyunsaturated fatty acids in vegetable oils, particularly linolenic esters in soybean oil, are especially sensitive to oxidation. A wide variety of naturally occurring oils and fats contain a mixture of olefinic compounds which vary in unsaturation and hence oxidizability from the singly unsaturated oleic to the polyconjugated oleostearic esters. This deterioration is generally due to their tendency to absorb or react with oxygen, and the observed rancidity results primarily from the products formed during oxidation. These products generally include unwanted peroxides, aldehydes, ketones and acids.
Aldehydes have been recognized for many years as the chemical agents responsible for deterioration of oils. These products have been shown to be derived from initially formed hydroperoxide. The primary initial products of the autoxidation of fatty acid esters, the hydroperoxides, appear to be odorless and flavorless. However, a host of carbonyl compounds, acids, and other products are formed, through decomposition and further oxidation of the hydroperoxides. Oxygen from the air first reacts with the unsaturated fatty acid esters at or adjacent to the double bonds to form hydroperoxides which then decompose to yield aldehydes having the pungent odor and flavor of rancid fats. Oxidation is catalyzed by light and metals such as copper or iron and is accelerated by heat. It would be desirable to reduce or eliminate the hydroperoxides to stop the subsequent reactions from occurring. There are uses for some of the vegetable oils that can accept the presence of hydrocarbyl phosphites. It has been found that the phosphites are effective in reduction of peroxide (and hydroperoxide) levels in vegetable oils in addition to the epoxidized vegetable oils.